1. Field of the Invention
The present invention relates to antennas. More specifically, the present invention relates to slot coupled, planar array waveguide antennas.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Planar array antennas are used for a wide variety of radar applications. A typical planar array antenna includes a linear array of coplanar radiating elements or slots in a radiating waveguide. Microwave energy is provided to the radiating waveguides by a feed waveguide running underneath the array of radiating waveguides and crosswise thereto such that there is a sharing of a section of broadwall.
Slot coupling is a frequently used technique for coupling energy from the feed waveguide to the radiating waveguides. This is illustrated in FIG. 1 which shows a typical conventional array antenna. Slot coupling involves communication of energy through a slot in a broadwall of the feed waveguide through a colocated slot in the broadwall of the radiating waveguide. Energy is typically provided to the feed waveguide by an input waveguide (not shown) located at either end of the feed waveguide or somewhere along the length thereof. In the antenna of FIG. 1, the coupling slot is centered, inclined in the common broadwall, and the radiating slots are longitudinal and offset relative thereto.
For planar antennas, the radiating slots are essentially shunt (parallel) elements. Thus, short circuit elements are placed beyond the first and last radiating elements at distance equal to one quarter the wavelength in the waveguide (at which the antenna will be operating) to terminate the radiating waveguide properly and achieve a desired radiating pattern. However, the coupling slots are series elements. Thus shorts, in the feed waveguide, must be located beyond the first and last coupling slots at distances equal to one-half the guide wavelength at which the antenna will be operating to achieve optimum, efficient output coupling and the desired radiating pattern. Hence, for proper spacing of the shorting elements, it may be necessary to lengthen the feed waveguide.
However, due to space constraints, it is often necessary to fold the ends of the feed waveguides as illustrated in FIG. 1. This adds to the weight and cost associated with planar array antennas. Further, in many cases, the folded short is implemented in a tapered waveguide section for further space savings. Unfortunately, the slot under a tapered section does not behave as a series element. Hence, the performance of such slots is difficult to predict.
Thus, there is a need in the art for an alternative to the use of folded feed waveguides which would provide a light weight, low cost slot coupled array antenna design.